We do have knowledge that Adam was withdrawn from school and home schooled.
Yes - but we don't have knowledge as to why he was withdrawn from school & homeschooled, other than a media report that stated that NL disagreed with a school board decision or something along those lines. Furthermore, AL went on to college after that, and seemed to have done well academically during his time @ Western CT University, so the homeschooling point is moot, IMO.
We do have knowledge that Adam had not spoken to either his father or brother in two years.
Cutting off contact with a family member is not a predictor of future violent behavior.
We do have knowledge that Adam was withdrawn socially
I think the key here is whether or not he was socially withdrawn due to Asperger's Syndrome, or some other affliction as yet unknown to the public.
had knowledge of and knew how to use his mother's arsenal of weapons, played violent video games and spent much time alone in the basement.
I agree that it's not healthy for anyone to spend the majority of their time in isolation, whether they're playing video games (violent or otherwise) or reading, or doing crossword puzzles, regardless of their circumstances. Isolation is not conducive to mental health.
Regarding the firearms: if it turns out that he'd been diagnosed with a mental illness, or if it turns out that he'd acted out violently in the past, then I'll be the first to say that it was a recipe for disaster. Unless & until we hear that AL was in fact mentally ill and/or violent in the past, I'll reserve judgment regarding the weapons in the home (which, btw, were purported to have been locked up when not in use @ the shooting range).
In hindsight, it's easy to point to these things and declare "Aha!!!" I've been guilty of doing that exact thing as I've followed this case. However, as I've calmed down and tried to be more objective, I've decided that these factors may or may not have had any significant bearing on AL's decision to murder 27 people.
We do know that his mother told a babysitter to never turn his back to Adam. We do know that his mother told friends that the situation was deteriorating.
I highly doubt that NL told the sitter not to turn his back on AL because she believed that AL would do harm to the sitter. It's been reported that AL had a pain insensitivity disorder (CIPA?). I think this was more than likely why she advised the sitter to pay close attention - to protect AL from potentially harming himself.
IMO, the triggering event for AL's homicidal rampage was the likelihood that his living arrangements were on the verge of changing. NL had been looking into placing him in a residential facility.